<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* 标签选择器 */
        p{
            color: red;
        }
        h3{
            color: blue;
        }
        /* 类选择器 */
        .hello{
            font-weight: bold;
            font-size: 35px;
        }
        .world{
            background: #ccc;
        }
        .b2{
            text-decoration: underline;
        }
        /* ID选择器 */
        #welcome{
            color: green;
            font-weight: bold;
            background: pink;
            width: 250px;
        }
    </style>
</head>
<body>
    <p>aaa</p>
    <div>bbb</div>
    <!-- 通过class属性来调用自定义的类选择器 -->
    <p class="hello world b2">ccc</p>
    <span>ddd</span>
    <div class="hello">eee</div>
    <p>fff</p>
    <span>ggg</span>
    <h3>hhh</h3>
    <!-- 通过id属性来调用自定义的ID选择器，id用来唯一的标识每个元素，值必须唯一 -->
    <h2  id="welcome">iii</h2>
</body>
</html>